The present invention relates to light conducting and light emitting tubes, herein referred to as "light tubes", and novel optical light films having an embossed prism pattern to contain and channel the light when formed into a tube. More particularly, the present invention is concerned with laminated tube construction and methods of constructing light tubes to achieve a wide range of illumination effects including the piping of light from an accessible, concentrated light source to distal areas and the release of such light in widely variable patterns.
Optical light films (OLFs) can be efficiently manufactured from polymers in flat, flexible, but fragile films and made to perform a myriad of illumination functions. The film can be formed into various tubular and other partially closed configurations by supporting it together with supplemental light controlling films or elements in preformed carrier tubing having light-permeable characteristics. For example, a sheet of OLF can be formed into a closed tube by disposing one longitudinal edge of the OLF adjacent the opposite longitudinal edge. Alternatively, a sheet of OLF can also be formed into a partially closed tube, for example having an arched cross-section, and maintained in such a configuration with a supporting structure. As used herein, the term "tube" is used broadly to include both closed and partially closed configurations.
In addition to carrying light from a source of illumination such as a high-intensity light bulb to a remote location, light tubes can also be used for emitting light over relatively large areas. For this purpose, various methods have been devised to direct light out of a light tube over portions of the tube length. One method involves placing a clear adhesive tape on the outer, grooved side of an optical light film. A clear tape placed in this manner reduces the internal reflectance of the optical light film in the taped area and essentially creates a window for "escaping" light. Another method simply involves removing a section of the optical light film where internal reflectance is not desired. Portions of a tube lacking optical light film will permit light to escape. A third method comprises forming a light tube with some means for directing the light at the walls of the optical light film at an angle greater than about 28.degree.. At such angles of incidence, the internal reflectance of the optical light film is greatly reduced. For example, the 3M Company of St. Paul, Minn., produces a product marketed under the name "X-70" which directs incident light at an angle of about 90.degree. to the angle of incidence. If a piece of "X-70" is positioned within a light tube, light moving generally along the longitudinal axis of the tube will be directed through the "X-70" substantially perpendicular toward a sidewall and out of the light tube. Another product, marketed under the name "SCOTCH-CAL EXTRACTOR FILM.TM.", directs light toward and through an opposite interior wall.
Since optical light film is fragile and sensitive to dirt and moisture, it is typically positioned within protective, outer tubes. Such tubes are generally transparent and can have a variety of finishess e.g. clear, matte, colored or opaque. The ability to insert the fragile optical light films into a carrier tubing, typically an extrusion product, is an impediment to the light tube designer. Moreover, shipping fabricated light tubes is costly because of their high volume relative to volume of component displacement and their inherent vulnerability to damage by breaking and scratching. Thus the low manufacturing cost of the critical optical film component is heavily offset by shipping costs. Also lost is the ability of the designer to achieve at acceptable cost finished products which feature many of the useful and underlying lighting functions which the optical light film is inherently capable of performing.
It would therefore be desirable to provide novel methods for forming light tubes and light tube products using the films which are cost effective, optically efficient and functionally varied.